DESCRIPTION: The goal of this project is to develop a specific binding protein that has antibody-like diversity, but is suitable for high-level bacterial expression and use in extreme environments. Production of recombinant antibodies in E. coli provides an inexpensive source of active protein for antibody-based technologies, and the small size of the recombinant antibody fragments provides significant advantages in some applications. However, there are disadvantages attributable to the mammalian origin of the complicated dimeric peptide structure of recombinant antibodies. The bacterial folding and secretion pathways often fail to yield high levels of functional expression, especially in the case of Fab. Also, the weakness of association between the variable domains often leads to stability problems, especially in case of single- chain Fv. The proposed specific binding protein has an "antigen binding site similar to that of antibodies in aspects important for binding and diversity, but are based on a natural bacterial protein of high thermostability. The proposed design is monomeric, and thus should circumvent folding, expression and stability problems associated with recombinant antibody fragments. It should be possible to recover binding-proteins of desired specificities from a diverse library of these molecules by phage display technology.